Remove misleading TODO comment about shakapacker.yml integration (#1962)

## Summary

Removes the TODO comment about automatic detection of
`server_bundle_output_path` from shakapacker.yml, as this feature was
never implemented and may not be feasible.

## Background

PR #1808 was titled "Auto-detect server bundle path from
shakapacker.yml" and contained a TODO comment referencing this feature.
However:

1. **The feature was never actually implemented** - the PR branch
contained the foundational work (server bundle security features), which
was already merged via PRs #1798 and #1815
2. **The concept may not be feasible** - Shakapacker's
`public_output_path` serves a different purpose than React on Rails'
`server_bundle_output_path`:
- `public_output_path`: Where webpack outputs ALL bundles (public
directory)
- `server_bundle_output_path`: Private server bundles OUTSIDE public
directory for security

## What's Already on Master

The server bundle security features are fully implemented and working:
- ✅ `server_bundle_output_path` configuration option
- ✅ `enforce_private_server_bundles` security enforcement
- ✅ Private server bundle path resolution logic
- ✅ Comprehensive test coverage

## Changes

- Remove misleading TODO comment from
`lib/react_on_rails/configuration.rb`
- Closes #1808 (which has been separately closed with detailed
explanation)

## Testing

- ✅ RuboCop passes
- ✅ No functional changes - only removing a comment

---

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Co-authored-by: Claude <noreply@anthropic.com>

Author: justin808

lib/react_on_rails/configuration.rb

@@ -51,9 +51,6 @@ def self.configuration
       server_bundle_output_path: "ssr-generated",
       enforce_private_server_bundles: false
     )
-    # TODO: Add automatic detection of server_bundle_output_path from shakapacker.yml
-    # See feature/shakapacker-yml-integration branch for implementation
-    # Requires Shakapacker v8.5.0+ and semantic version checking
   end
 
   class Configuration